Introduction
Differential scanning calorimetry is a common method for studying the curing process of thermosetting polymers. By measuring the heat flow change during the curing reaction, information such as reaction heat, curing temperature and kinetic parameters can be obtained. These data are of reference significance for material formulation design, process optimization and performance evaluation.
Rationale
The basic principle of differential scanning calorimetry is to measure the heat flow difference between the sample and the inert reference under programmed temperature control. When a thermosetting polymer undergoes a curing reaction, heat is usually released, which manifests as an exothermic peak on the heat flow curve. By integrating the area of the exothermic peak, the enthalpy change of the reaction can be calculated. The heat of reaction ΔH can be calculated by the following formula:
ΔH = K × A / m
where K is the instrument constant, A is the exothermic peak area, and m is the sample mass.
Experimental methods
Before testing, the instrument needs to be calibrated for temperature and thermal enthalpy, usually using high-purity indium, zinc and other reference materials. Sample preparation should be representative, generally between 5 and 15 mg, and placed in a closed pressure-resistant crucible to avoid volatile escape. The test often adopts the dynamic heating mode, and the heating rate is mostly set in the range of 5 to 20 °C/min, and the atmosphere is usually nitrogen. Repeat testing is recommended for each sample to confirm repeatability.
Data analysis
A typical differential scanning calorimetry curve provides multiple characteristic parameters. The start, peak, and end temperatures reflect the temperature range of the curing reaction. The heat of reaction is directly related to the degree of curing. By changing the heating rate and using kinetic analysis methods, the activation energy of the reaction can be further estimated. When analyzing the data, attention should be paid to the consistency of baseline delineation.
| Characteristic parameters | Physical significance |
| Starting temperature | The temperature at which the curing reaction begins to occur |
| Peak temperature | The temperature at which the reaction rate reaches its maximum |
| termination temperature | The temperature at which the curing reaction basically ends |
| Reaction heat | The heat released during the curing process of a sample per unit mass |
Influencing factors
Test results are influenced by a variety of factors. Increased rates of warming often result in a shift in the characteristic temperature towards higher temperatures. Excessive sample mass can lead to temperature gradients due to heat conduction constraints. Sample morphology and granularity affect heat transfer and reaction uniformity. Atmosphere type and flow rate may also have an impact on certain material systems with oxidative or volatile side reactions. When conducting comparative studies, the consistency of experimental conditions should be strictly controlled.
Application examples
This technology is widely used in the research and development and quality control of thermosetting materials such as epoxy resin, unsaturated polyester, and phenolic resin. For example, in epoxy systems, measuring the heat of reaction under different formulations or different curing agents can help evaluate the reactivity of the curing agent or estimate the maximum cure. In the formulation of composite materials, the curing reaction heat data can provide a basis for setting the heating power of the mold.
Summary
Differential scanning calorimetry provides a direct and effective means to characterize the curing heat of thermosetting polymers. Through standardized experimental operation and rigorous data analysis, reactive heat data with good reproducibility can be obtained, which serves the material development and production process.
References
1. The application basics of thermal analysis, involving the principle and calibration of differential scanning calorimetry.
2. Thermal analysis of polymer materials, related to the curing kinetics of thermosetting resins.
3. International standard ISO 11357-5, on the determination of reaction heat and reaction temperature by differential scanning calorimetry of plastics.
4. Several journal technical articles on the curing behavior of epoxy resins.